You can't bulk change that option on all pages. But what is the purpose of doing this? Running sequentially the request is normally something that needs to be done on specific use case and not in general. Could you tell us why you would need to do that on all your pages?

Actually I have prepared a script which will upload 100 files into my application. While replying the script with default option i.e., "In parallel-HTTP compliant", the pages are executing parallel. But the executing pages requires some dynamic values from the previous pages which are yet to start execution. Because of this that particular page is getting failed. But after completion of script execution, you can see all dynamic values in variables.

Indeed requests inside the same page are executed in parallel. But pages are executed sequentially. So in your example i do not see why request2 is executed if requests is stil in progress. Unless you put your page under fork logical action. Is it the case?